The present invention relates to a sheet material feeding apparatus that intermittently feeds a sheet material a predetermined quantity by a predetermined quantity to a press apparatus, and more particularly to a sheet material feeding apparatus suited to feeding of a sheet material, which is used for manufacturing small-sized parts used in information associated equipment such as personal computers, etc., to a press apparatus at high speed with high accuracy.
Conventionally, there are known sheet material feeding apparatuses comprising a pair of upper and lower rolls that interpose therebetween and feed intermittently a sheet material to a press apparatus, a roll clearance adjusting device that adjusts a clearance between the both rolls according to the thickness of a sheet material, and a release device that temporarily releases a sheet material, having been interposed by the both rolls, just before a sheet material fed to the press apparatus is subjected to press working, the pair of rolls comprising a main roll driven by a drive motor and a sub-roll driven through a sheet material by the main roll (see, for example, U.S. Pat. No. 5,720,421).
Also, there is known a sheet material feeding apparatus (see, for example, U.S. Pat. No. 5,720,421), in which a servomotor is used as a drive motor for driving of a main roll, and a sheet material feeding apparatus (see, for example, JP-U-3-57414), in which a drive motor having an annular stator and an annular rotor is constituted as a main roll.
The release device performs the function of temporarily releasing a sheet material in synchronism with the operation of a press apparatus, that is, the sheet-material releasing function. That is, there are some metal mold devices for press apparatuses, in which a pilot pin directed downward is protrusively provided on an upper metal mold and just before the upper metal mold and a lower metal mold are caused to butt against each other to permit press working, the pilot pin is inserted into a positioning hole beforehand formed on a sheet material to enable positioning the sheet material relative to the metal mold device with high accuracy. In order to position the sheet material with the use of the pilot pin, it is required that a sheet material feeding apparatus releases the sheet material from the pair of rolls at the time of positioning. The release device is provided to produce such function.
The U.S. Pat. No. 5,720,421 describes a construction of the release device, which comprises a wedge member having an inclined surface inclined at a predetermined angle and a follower connected to a sub-roll to engage with the inclined surface of the wedge member and in which the wedge member is moved axially of the sub-roll by a drive device to displace the sub-roll up and down through the follower, thereby generating the sheet-material releasing function.
The construction having the wedge member and the follower also generates the function of adjusting a clearance between the both rolls according to the thickness of a sheet material, that is, the roll clearance adjusting function.
In the release device described in the U.S. Pat. No. 5,720,421, the follower engages with the inclined surface, which is inclined at a predetermined angle, and when the wedge member is moved axially of the sub-roll, the follower in engagement with the inclined surface of the wedge member is displaced up and down by a magnitude in proportion to shift of the wedge member and the sub-roll is displaced up and down by a magnitude corresponding to the displacement of the follower. That is, horizontal shift of the wedge member and vertical displacement of the sub-roll are linearly related to each other. Accordingly, it is difficult to perform control so as to smooth actions at the start (that is, when the sub-roll begins a vertical displacement) and at the time of stoppage (that is, when the sub-roll stops a vertical displacement) and there is a fear that vibrations occur to lead to degradation in accuracy of feeding, in particular, when the sheet material feeding apparatus is operated at high speed.
Also, that construction, in which the wedge member and the follower causes vertical displacement of the sub-roll, is both one that generates the sheet-material releasing function and one that generates the roll clearance adjusting function and by operating the same drive device, the respective functions are generated, but there is a fear that it becomes difficult to appropriately control the drive device so as to generate the both functions appropriately.
For example, in order to enable feeding sheet materials having various thicknesses, let assume that the roll clearance adjusting function is required to generate a vertical displacement of a sub-roll within the range of 1 mm to 5 mm. Even in such case, it suffices that a vertical displacement of a sub-roll required to generate the sheet-material releasing function be in the order of 0.05 mm to 0.1 mm. In this manner, there is usually a large difference between the range of displacement of a sub-roll required to generate the roll clearance adjusting function and the range of displacement of a sub-roll required to generate the sheet-material releasing function. Generally, in the case where a distance of displacement is large, it is required to increase a displacement speed and in the case where a distance of displacement is small, it is required to make a displacement accurate rather than to increase a displacement speed, but it is difficult to appropriately control a single drive device so as to meet different demands in this manner.